Manufacture of rubber



Patented Feb. 21, 1939 MANUFACTURE OF RUBBER Henry Potter Stevens,London, England, assignor, by mesne assignments, to George R. Beach,Jr.,

Chadds Ford, Pa.

No Drawing. Application October 1, 1932, Serial No. 635,852. RenewedMarch 19, 1937.

Great Britain October 9, 1931 6 Claims.

This invention concerns the manufacture of shaped articles of softvulcanized rubber possessing a high and variable degree of flexibilityand resilience and an improved resistance to oil absorption.

"According to the invention, a shaped vulcanized soft rubber article isproduced, which is characterized by the presence therein of a highproportion of an oleaginous softener, that is to say, an oily or fattysubstance normally fluid or.

of low melting point.

The invention has particular reference to an improved manufacture ofprinters rollers and like printers devices.

The usual printers rollers of gelatine composition have a number ofdisadvantages, notably uncertainty of life and sensitivity to changes inatmospheric humidity and temperature; and the proposal has been made toreplace the gelatine by vulcanized rubber associated with rubbersubstitute (pre-vulcanizedunsaturated fatty oil) and the usualcompounding ingredients, this alternative aiming at providing a rollerof greater permanence and of increased oil-resisting properties. In thisalternative there is a limit set in practice to the proportion of rubbersubstitute and consequently to both thevariability in the softness andthe degree of oil-resistance of the product. The present inventionprovides a printers roller of improved resistance to atmosphericchanges, a Wider variability in resilience and softness and increasedresistance to oil-absorption. Such rollers and the like also do not needthe constant cleaning which is necessary in the case of similar articlesof gelatine.

A shaped article of soft rubber, for example, a printers roller,according to this invention may comprise or consist of a vulcanizedplastic provided by a vulcanized mixture of rubber and a high proportionof oil or derivatives thereof.

The softener may be a mineral oil or an appropriate low-meltingderivative such as mineral jelly, or a mineral oil in association withsaid type of derivative; or may be an animal or vegetable oil, or amixture of mineral and fatty bodies. Since permanency is a quality to bedesired in the product, the softening agent should be one which issubstantially non-volatile between reasonable temperature ranges.Substantially non-volatile hydrocarbon oils meet this condition,examples of suitable oils of. this class being transformer oil andlubricating oils, especially spindle oil. It has been found thathydrocarbon oil fractions, such askerosene, which contain componentsvolatilisable on comparatively moderate rise of temperature, whilecapable of giving primarily a rubber composition of the typecharacterising the present invention, possess the disadvantage justmentioned by reason of loss with time of at least a part of the oilcomponent with a consequent shrinkage of the product.

Palm oil and olive oil are examples of suitable vegetable oils.Vegetable oils of solid character, such as palm oil, tend, if used alonein high proportion, to give rather hard final products, and in suchcases there may be a practical limit set to the quantity of oilutilisable alone. For example, 100 per cent. (relatively to the rubber)of palm oil alone gives a rather hard moulded product when the mixing isvulcanized under the conditions usually employed to produce soft rubber.Hence such a softener is unsuitable when used by itself, and it may benecessary to use oils and other softeners of the character of palm oilin conjunction with other softeners of more fluid nature. Theproductionof over-hard products tends also, but in a higher degree, to follow theuse of high melting point waxes and solid fats and fatty acids.

The type of composition according to this invention may possess theproperty, derived from the presence of an adequately high proportion ofoleaginous softener, that they can be cast at ordinary temperature or ata comparatively low raised temperature, that is one not much exceeding100 0., in the form of a parent mixing compounded from solid rubber. Itwill be appreciated, however, that the ease of moulding themother-composition may be influenced by the character and content of theother ingredients of the mixing.

One type of composition according to this invention consists of, avulcanized product characterised by great softness combined with a highdegree of resilience, and such material is especially applicable to themanufacture of facemasks, surgical pads, childrens toys, soft rubberlinings, coatings and cushions, sound and shock absorbers, and otherarticles wherein a high measure of softness and resilience aredesiderata. The flexibility of these products and the fact that they canbe made of very varying degrees of softness render them especiallysuitable for different kinds of surgical pads and like uses. The harderbodies are suitable for inking rollers for printers, and other uses forwhich the softer known rubbers are employed. Both types of material areparticularly applicable to cases wherein the rubber is liable to comeinto contact with oil.

is preferably reserved to a separate stage.

The compositions according to this invention may comprise fillers, whichmay be mineral or organic, and also colouring matter and othercomponents such as are known in the art; and the final composition maybe porous or microporous, opaque or translucent.

The invention comprises a process of manufacture of shaped soft rubberarticles which is characterised by directly compounding rubber with anoleaginous softener in high proportion and with vulcanizing agents, withor without other ingredients as aforesaid, shaping the mixing, underapplication of moderate heat as required, and vulcanizing the mixing.

Vulcanization may be effected in the open and, by aid of suitableaccelerators, at comparatively low temperature, i. e. one notsubstantially exceeding 100 C. but may be also carried out underpressure and high temperature.

According to one embodiment of said process of manufacture, solid rubberis directly compounded to a homogeneous mass with an oleaginous softenerin high proportion and with vulcanizing agents, together with such othercomponents as are desired, and the mixing is shaped and vulcanized.

Alternatively, the rubber may be in the form of an aqueous rubberdispersion, such as rubber latex; and in this case an emulsifying agentmay be employed for the better homogenisation of the aqueous materialand the softener.

The use of an aqueous rubber dispersion has the advantage that all theconstituents of the primary mixing can be free-flowingat room tem- I"perature. The mixing can therefore be very easily filled into a mouldand air-pockets can be readily eliminated. Care must, of course, beobserved that the rubber dispersion does not coagulate appreciablybefore it is introduced into the mould. The use of ingredients indispersed form, as, for instance, an emulsion of the softener in rubberlatex, has several advantages over dry mixes in that, the dispersionsbeing naturally free-flowing, ingredients, including softeners, solid atordinary temperatures can be used without adverselyalfecting thefluidity of the mixing. Thus, for example, emulsions comprising waxesand bitumens may be used with due allowance, as explained above, for thenecessity of a limited proportion.

When ordinary raw rubber is used, it may be milled in the customarymanner and directly dispersed with the aid of heat in the softener, withor without the usual compounding ingredients as may be desired, but theaddition of the accelerator Since it is difficult to attain homogeneousdispersion of the rubber in the cold within a practicable time, theadmixture with the softener is preferably effected under application ofheat. The accelerator, which may'conveniently be previously admixed withsome softener, e. g. the same softening agent as compounded with therubber, is subsequently added. The accelerator may also be introducedotherwise than distributed in a part of the softener, provided thatuniform admixture with the main body of the materials is attained andrisk of scorching is avoided. Likewise the other compounding ingredientsmay be added at any convenient stage, and may be worked in with therubber or the softener in the first place or partly in the one andpartlyin the other.

The use of certain softening agents in rubber for the purpose ofobtaining soft rubber and also for facilitating mixing has been knownfor a long time. Thus for the said purpose and also for the productionof materials for other specific ends, the addition of wax, such asparaffin wax and montan wax, with or without oil, has been proposed. Inthe ordinary use of true softening agents as previously known themaximum proportion relatively to the rubber may be said to be about 25per cent. for special types of mixings such as are employed for spongerubber, the usual proportion being about 5 per cent. or less. Theseconsiderations apply to the compounding of ordinary raw rubber. In thecase of aqueous rubber dispersions, such as latex, the addition of oilslikewise usually in comparatively small proportion, has also beenproposed. The percentages in such cases have amounted to but notexceeded on the weight of the rubber, as heretofore practised.

According to the present invention a very much higher proportion ofoleaginous softener is introduced into the rubber than has hitherto beenconceived to be possible or practicable. Such proportion, like that ofother components of the mixing, may be varied over a wide range and noabsolute. numerical rule can be laid down, but as a'practical guide itmay be said that the lowest proportion of oleaginous softener, expressedrelatively to the rubber, is such that, in contradistinction to knownpractice with raw rubber, the final mixing is unsuitable for feasibleworking on the ordinary mixing rolls. Thus, it has been found that withspindle oil the maximum amount which could be incorporated-although withdifficultywith 100 parts of rubber on ordinary mixing rolls was about 70parts, and a somewhat higher proportion in the presence of 100 parts ofmineral filler (equal weights of clay and whiting). The products weresoft, sticky masses which, although easily shapable, could barely becast by pouring up to a temperature of C. For a mobile oil, such asspindle oil, therefore, a high proportion is. to be regarded as upwardsof approximately 70 per cent. relatively to the rubber, and largerproportions of more viscous softeners must be used to obtain mixings oflike viscosity.

The variation in the proportions of the mixing components is, of course,to be determined by the physical properties of the final compositionsdesired; and the degree of softness to be sought may vary from that ofwhat is technically known as soft vulcanized rubber to softer productssuch as some of the gelatine compositions now in use.

I have found that the advantages in printers rollers manufactured fromrubber compounded with a high proportion as aforesaid of oleaginoussoftener are not confined to compositions comprising a mineral oil orother individual oil alone. Not only by varying the proportion ofsoftener, but also-by varying the composition thereof, it is easilypossible to obtain bodies of the different degrees of resiliency andsoftness previously indicated and always of much improved resistance tooil-absorption. When, according to this invention, a vulcanizablevegetable oil is employed, the oleaginous softener in the finishedcomposition may consist of or comprise vulcanized oil; but the productis distinguished from that obtained by the incorporation'of rubbersubstitutes with rubber in that said product will always contain a muchhigher proportion of oleaginous softener or even of Vulcanized oilalone, the direct incorporation of the softener. with the rubberfollowed by vulcanization of the mixture permitting the introduction ofa much higher proportion of oil, with a consequent increase ofoil-resistant properties in the product, wider variation in the degreesof softness,

w setting or vulcanization takes place.

and, in addition, greater facility of manufacture, since the parentmixing can be prepared fluid and hence be readily manipulated. It willbe appreciated that these advantages of improved oilresistance,variability of softness and greater ease of manufacture also apply toarticles according to the invention which do not contain vulcanized oil.It is readily possible by preliminary trial so to adjust the relativequantities of the mixing components as to give a mixing which, by reasonof an adequately high proportion of softener, can be cast at moderatetemperature (that is to say, between normal temperature and one notsubstantially exceeding 100 C.) and provide a final composition of asoftness between the limits previously indicated. It will be appreciatedthat the temperature at which the mixing may be conveniently cast is notsolely dependent upon the proportion of softener present since thenature and amount of the other compounding ingredients in the mixing mayalter its degree of mobility, and consequently a higher temperature maybe necessary in order to make the mass sufficiently freefiowing to bemoulded under practical conditions. The pasty-like mixings referred toabove are adaptable to such shaping methods as extrusion; but forordinary mould-shaping the proportion of softener must be such as torender the mixing sufficiently mobile to fill the interstices of themould and to find its own level at or below the temperature at whichsetting or vulcanization takes place. In most cases it has been foundpossible to use a mobile softener, such as spindle oil, and in suchproportion that the mixing can be described as being at normaltemperature a fluid rather than a plastic solid or a paste; but in othercases where it may be desired to reduce the proportion of liquidsoftener or to use a more viscous material or a normally solidsubstance, such as petroleum jelly or palm oil, the mixing may not bemobile at room temperature but may be a solid, a viscous or a pasty masswhich flows readily only at artificially raised temperaturewhich may,with convenience, be adjusted to be that at which It will be clear thatthere is no limit to the fluidity or solidity of the oleaginous softenerused provided that the mixing melts and becomes fluid so that it may becast before setting or vulcanization begins.

The lower limit of temperature is conditioned only by that requisite toshape the mixing, and, if desired, also to effect setting orvulcanization. If the mixing itself be a liquid which will find its ownlevel at room temperature the temperature to l which the mixing issubjected need be no higher than that required to effect setting orvulcanization within the desired period.

It will be apparent, therefore, that the minimum amount of softener inthe mixing will depend on (1) the viscosity, fiuidity or mobility of thesoftener employed; (2) the temperature to which it is possible to heatthe mixing before setting begins; (3) the particular accelerators ofvulcanization and other vulcanizing ingredients which control thetemperature at which setting begins; and (4) a time factor which is alsodependent upon the vulcanizing ingredients.

The higher limit of temperature is restricted by the tendency todecomposition of the rubber or other ingredients of the mix, and thetendency to form gas pores or bubbles, which result in a porous product,although in some cases it is desirable to employ a higher temperaturethan is otherwise ous product. It will, however, be obvious to thoseskilled in the art that in most cases it is desirable to work atrelatively low temperatures and to use powerful accelerators orcombinations of these, as at higher temperatures gas bubbles will formmore readily than in the known processes of vu1- canizing in which thematerial is enclosed and vulcanization takes place under excesspressure.

The vulcanization of the parent mixing may, as already stated, beeffected at low temperature and in the open by the known procedure ofin- 3-? eluding ultra-accelerators in the mixing; and vulcanizationunder these conditions may be regulated by the combined use of a mixtureof accelerators, for example, a reagent of a semi-ultraaccelerator type,an instance of which is mercapto- Example I A mixing as follows:-

. Parts by weight Rubber 100 I Sulphur 5 Zinc oxide Palm oil 10 was madeon the mill, and was then dispersed in 360 parts by weight of spindleoil with the aid of gentle heat, and to the dispersion thus obtainedthere were added, with uniform mixing of the materials during theaddition, two parts by weight of diphenylguanidine and one part ofmercaptobenzothiazole distributed in a little high-boiling naphtha.

The mixture, which was of a viscosity to allow of slow flowing atordinary temperature, was poured into a round-bottomed basin and wasvulcanized by heating in the open for 2 hours on a water-bath. Theproduct was a buff-coloured, lenticular-shaped object, which was verysoft but firm and resilient, and suitable for a surgical pad.

Example II A mixing as follows:-

Parts by weight Rubber 100 Sulphur 5 Zinc oxide Lithopone 10 Redcolouring matter 0.0375 Palm oil 20 was worked up on the mill, and thendispersed in 300 parts by weight of spindle oil. To the dispersion wereadded, with careful mixing as before, two parts by weight ofdiphenylguanidine and one part by weight of mercaptobenzothiazoledistributed in 10 parts by weight of spindle oil.

The product was a flesh-coloured viscous mass, very slow-flowing at theprevailing temperature but flowing readily on warming on the waterbath.The mixture was poured into an ordinary open cake-mould and wasvulcanized on the waterbath at 100 C. as before. The product wasflesh-coloured, soft-although somewhat firmer than the produce ofExample I-and highly flexible.

Example III A mixing as follows Parts by weight Rubber 100 Zinc oxide 10Palm oil 25 was worked on the mill and stirred into parts by weight ofsulphur distributed in 1'75 parts by Weight of petroleum jelly oversteam. One part by weightof diphenylguanidine and 0.5 part by weight ofmercaptobenzothiazole were subsequently added. The mass, moulded toshape, was vulcanized by heating at 100 C. for 2 hours. The product wasa soft, compact, firm and elastic vulcanized rubber of a brown colour,suitable for printers rollers and like uses.

Example IV A mixing as follows Parts by weight Rubber 100 Sulphur 4 Zincoxide Palm oil 100 was worked up in an internal mixer, 2 parts ofdiphenylguanidine and 1 part ofmercaptobenzothiazole being subsequentlyadded. As already explained, this mixing was over-viscous by reason ofthe sole presence in high proportion of palm oil. A part of the mixingwas put into a mould and allowed to spread into position whilevulcanizing at 100 C, the total period of vulcanization being 1 /2hours. The product was dullbrown in colour, and relatively hard andstiff, being nearly as hard as what is technically known as a softvulcanized rubber. It was of a nature suitable for making solid rubberballs, printers rollers, door-stops and like uses.

Example V A mixing as follows:

Parts by weight Rubber Sulphur 1.5 Zinc oxide 1.5 Petroleum jelly 100.0Diphenylguanidine 0.3 Mercaptobenzothiazole 0.15

was prepared and treated as in Example III, except that the time ofvulcanization was 1 hours. The product was of a lightyellow colour, verysoft and flabby, with a surface tending to become slightly sticky.-

Example'VI An ultimate mixing as follows:-

. Parts by weight Rubber 100 Sulphur1 75 Zinc oxide Whiting 100 Palm oil50 Spindle oil 400 Zinc diethyldithiocarbamate 4.0

was moulded to shape and vulcanized at 100 C. for 16 hours. The materialobtained was dark reddish-brown, slightly porous, flexible anddeformable, and harder than any of the foregoing products and, althoughcontaining, as shown, a high proportion of softeners", somewhat brittle.During vulcanization, some oil sweated to the surface. This product isalso particularly suitable as material for printers rollers.

Example VII An ultimate mixing as follower- Parts by weight Zincisopropylxanthate 3.0

was made up. The dispersion of the rubber in the olive oil was muchslower than when mineral oil was used. The mixing was vulcanized at 100C. for 3 hours. The product was fleshcoloured, very soft and flexibleand had a somewhat sticky surface.

Example VIII To a mixing as follows:-

Rubber latex (about 40 per cent. dry rubher) c. c 250 Sulphur -grams 3Zinc oxide do 20 Pi p e r i d i n e pentamethylenedithiocarbamate grams0.5 there were added 150 c. c. of spindle oil and 10-20 0. c. ofglycerine. An emulsion was formed on shaking. This was poured into anornamental open mould, and was heated therein in a wateroven for 1 hour.solid, soft, elastic mass reproducing the shape of the mould. Somemoisture was lost during the process.

Example IX To 250 c. c. of rubber latex (about 40 per cent. dry rubbercontent) a few drops of concentrated ammonia solution (0.880) were addedand then three parts of colloidal sulphur paste of 50 per cent.concentration, 5 parts zinc oxide and 0.5

part of piperidine pentamethylenedithiocarbamate. Into this mixturethere were rapidly stirred 100 parts of cod-oil, and the mixtureimmediately' cast in an open cake-mould, because it was found thatcoagulation set in rather rapidly. The mould was heated for 1 hours at90 C. There was obtained aproduct of biscuit colour which, althoughsoft, was substantially firm and sharply moulded.

The products obtained according to both the immediately foregoingexamples are suitable for printers rollers'and like devices.

If desired, instead of employing hot-vulcanization methods in theproduction of the rubber article, other known vulcanization processesmay be used, for example, the cold cure process. Thus, a vulcanizedproduct may be obtained by merely pouring a small quantity of undilutedsulphur chloride into the liquid oil-rubber mixture and stirring well.Upon casting the resulting mixture the latter sets in a short time to avulcanized product closely resembling the products of the foregoingexamples.

I claim:

1. A vulcanized compound composed of vulcanized rubber materialcompounded from raw rubber or rubber substitute, a non-volatileoleaginous' softener, a reinforcing material such as zinc oxide, andhot-cure vulcanizing and accelerating ingredients sufficient to effectvulcanization of rubber, the combined proportions by The product was apale yellow,

weight of said rubber and reinforcing material being less than theproportion of said softener and such that the mixture will fiow underpressure, and the amount of softener not exceeding three times theweight of the rubber.

2. A vulcanized compound composed of vulcanized rubber materialcompounded from raw rubber or rubber substitute, a non-volatilenondrying oleaginous softener, a reinforcing material, and hot-curevulcanizing and accelerating ingredients sufficient to effectvulcanization of rubber, the amount by weight of said rubber beingsubstantially half the amount of the softener.

3. A vulcanized compound composed of vulcanized rubber materialcompounded from raw rubber or rubber substitute, a non-volatile01eaginous softener, a reinforcing material, and vulcanizing andaccelerating ingredients sufficient to effect vulcanization of rubber,the combined amounts by weight of said rubber and reinforcing materialbeing approximately half the amount of the softener.

4. A vulcanized compound composed of vulcanizable rubber-like material,a non-volatile oleagino-us softener, a filling material, and hotcurevulcanizing and accelerating ingredients sufficient to effectvulcanization of the rubber material, the amount of said softener beingsufficiently greater than the combined amounts of rubber material andfiller to produce a mixture, before vulcanization, capableof beingflowed into a mold.

5. A vulcanized compound composed of vulcanizable rubber-like material,a non-volatile oleaginous softener, a filling material, and hotcurevulcanizing and accelerating ingredients suflicient to effectvulcanization of the rubber material, the amount of said softener beingsufficiently greater than the combined amounts of rubber material and.filler to produce a mixture, before vulcanization, capable of beingflowed into a mold, and the amount of said filling material being lessthan the amount of rubber material.

6. A vulcanized compound composed of vulcanizable rubber-like material,a non-volatile oleaginous softener, a filling material, and hotcurevulcanizing and accelerating ingredients sufficient to effectvulcanization 0f the rubber material, said rubber material being equalat least to one-third but not exceeding the amount of said softenerwhereby to produce a mixture before vulcanization which is sufficientlyfluid to flow intothe cavities of a mold.

HENRY POTTER STEVENS.

